This invention relates to hole filling, self-locking and self-sealing plugs made of injection moldable plastics and to a method for making same.
In the manufacture of automobiles, refrigerators, stoves and other appliances there are metal panel portions such as automobile floor pans, door panels or other vertically oriented panels that contain openings, or holes, of various shapes and sizes to provide for tool access through the hole to enable assembly of the panel to its supports or the attachment of other components of the automobile or appliance to an interior surface of a panel. After assembly, it is necessary to fill the opening to restore the original panel contour. Heretofore, metal plug stampings have been used and such stamped plugs have been fastened in place by hot melt adhesives, by welding, brazing or by screws or the like through overlap portions of the replacement metal plug and the panel. Such metal replacements require preliminmary fabrication of the replacement plugs and manual assembly which is time consuming, expensive and labor-intensive, all of which is desirably eliminated.
The plugs of this invention are suitable to replace the heretofore used metal plugs and eliminate much of the previously required labor by fabricating the plugs from compatible plastic materials that are each thermoplastic and chemically similar, and which are configured so as to be insertable into a hole or opening in a panel by snapping the plug through the opening, to simultaneously lock the plug in place and seal against the inner periphery of the opening.
The pluqs are self-locking and self-sealing and are fabricated from injection-moldable plastic components selected so as to provide all of the properties necessary to enable safe use in vehicles, etc., including high tensile and impact strengths, high resistance to dislodgement from concentrated forces applied to the central hole-filling portion of the plug from either side of the panel, high resistance to penetration or puncture particularly from an exterior applied force, and sealing resistance to leakage of moisture, gases or water through the opening.
The hole filling-locking portion is formed from a material having the requisite strength and hardness to make the plug self-locking and resistant to dislodgement and impact and penetration resistance over the range of temperatures of intended use, and the sealing portion is made from a chemically compatible material having the required resilience to permit sufficient deformation when pressed against the inner periphery of the opening to facilitate insertion of the unitary plug into the opening and to provide the required sealing between the resilient peripheral portion of the plug and the inner peripheral surface of the panel opening in a manner generally similar to the sealing of the grommet of U.S. Pat. No. 4,081,879.
The method of this invention is a process of injection molding two compatible thermoplastic materials into a mold which unite in the mold upon cooling to form a unitary plug. The plug is fabricated from two separate but chemically compatible thermoplastic injection moldable materials by co-injection, comprising the steps of injecting material having metal-like properties to form the hole filling and locking portions, slightly cooling the locking portion, injecting the resilient, softer material into the same mold into contact with the still hot, locking portion to form the sealing portion, and further cooling both portions to thus form the unitary dual durometer plug of this invention.